This invention relates generally to hydraulic brakes and clutches, and more particularly concerns a combined hydraulic brake and clutch which is of a failsafe design, and which is offered in a compact, self-contained package.
In power trains for cranes, a hydraulic brake is often provided for controlling the rotation of a shaft involved in lowering and raising loads. One such brake which has met with considerable commercial success is that disclosed and claimed in U.S. Pat. No. 3,863,038 and in U.S. patent application Ser. No. 801,085 filed May 27, 1977. In these installations at present, the brake is actuated so that the brake itself is pressurized and braking action is eliminated while the shaft rotates. When load moving action is terminated, the brake moves to a shaft-engaging position so as to hold the load.
In cranes and hoists, considerable mechanical advantage is provided throughout the entire drive system, and thus a small system output displacement requires a large input displacement. When the brake is located on or near a large crane or hoist cable drum, any time delay in applying the brake, or any slight retrograde or reverse motion at this position may permit the load to drop some distance. In large cranes or hoists, this load may drop two or three feet before upward motion again begins.
When using such a crane in precise work, this initial load drop is unacceptable. For example, when a large crane or hoist is being used for erecting structural steel, it may be necessary to raise a beam and hold it with considerable precision in order to fit the beam to adjacent columns or other members.
It is therefore desirable to offer not only a hydraulic brake in these power trains, but also a device such as a unidirectional clutch to prevent this momentary load drop in applications involving these cranes, hoists and the like.
While such units can be provided separately, their installation may be difficult, for generous room is not often provided for accommodating these power train elements in the crane.
It is accordingly the general object of the invention to provide a combined shaft brake and one-way clutch in a single, compact housing. A related object is to provide such a unit which incorporates a failsafe design.
Another object of the invention is to provide a combination of the brake and one-way clutch unit which permits an output shaft to be rotated without substantial impediment in one direction, while permitting close control of shaft rotation in the opposite direction. More particularly, shaft rotation in this opposite direction can be entirely prohibited or can be permitted to occur at a slow, gradual rate. A related object is to offer this shaft motion control even under great torque loads such as those found in lifting heavy loads by cranes.
A further object is to provide a powerful shaft-holding action in this unit.
Yet another object of the invention is to provide such a unit in which effective braking action can be applied against an output shaft only when that output shaft is rotated in a given direction. When the shaft is rotated in the opposite direction, the rotation occurs without braking action being applied.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.